1. Field of the Invention
The present invention relates to a method for preparing rocket propellants. More specifically, the present invention is a method for preparing a low-storage temperature bipropellant combination that provides for reduced power budgets devoted to propellant warming and offers significant improvements in safety operations combined with high performance. This enables, for example, missions to the outer planets on lower power budgets than is currently possible. This propellant technology also has applications in upper stage orbital maneuvering requiring high-performance, low temperature bi-propellants.
2. Description of Related Art
As a spacecraft moves farther from the sun, less radiant heat is absorbed and the temperature within insulated fuel tanks decreases. Thermal Control Systems (TCSs) are required to prevent fuel and oxidizer from freezing when they are not in use and to heat them to operating temperatures between 16 and 26° C. before use. For distances from the sun greater than 3 AU, the portion of the power budget consumed by heaters to prevent propellant freezing increases significantly.
With planned missions demanding more science for less money, the power budget necessary for propellant heating must be minimized to avoid limiting mission objectives. There is, therefore, a need for propellants having very low freezing and operating temperatures. Fuels and oxidizers having low freezing points such as Liquid Hydrogen (LH) and liquid Oxygen (LOX) are not suitable for use on planetary probes because they require cryogenic storage vessels capable of containing them within several AU of the sun. Propane is a gaseous hydrocarbon that readily liquefies by compression and cooling, melts at −189.9° C. and boils at −42.2° C. These physical properties make it a potential low-temperature propellant. MON (mixed oxides of nitrogen) is a solution of nitric oxide (NO) in dinitrogen tetroxide/nitrogen dioxide (NTO). MON propellants are used oxidizers on some military and commercial satellites. The freezing points of existing MONs are not low enough to be ideal candidates for use on deep space missions.
Gelling of rocket propellants has been accepted in the last decade as a method of improving performance and reducing environmental impact. For example, U.S. Pat. No. 6,013,143 (Thompson) discloses hypergolic fuel bipropellants containing inhibited red fuming nitric acid (IRFNA), nitrogen tetroxide (NTO), hydrogen peroxide, and hydroxyl ammonium nitrate oxidizers and monomethyl hydrazine (MMH), dimethylaminoethylazide, pyrollidinylethylazide, bis(ethyl azide) methylamine fuels gelled with silicon dioxide, clay, carbon, or polymers. U.S. Pat. No. 6,165,293 (Allan) discloses a thixotropic IRFNA gel oxidizer for use in hypergolic fuel bipropellants. U.S. Pat. No. 6,652,682 (Fawls) discloses gelled bipropellants doped with nano-sized boron particles.
The above patents disclose gelled propellants having improved safety and reduced environmental hazards compared to non-gelled propellants. The gelling of propellants to lower freezing points, operating temperatures, vapor pressures, or tankage weights is not disclosed.